At present, lithium ion batteries are required to be thinner and thinner as well as have higher and higher energy density, which demands a lithium ion battery has as much energy as possible in a volume as small as possible.
In conventional design of a lithium ion battery, a lead is a component soldered on a current collector to conduct current. Arrangement of the lead will increase the thickness of the lithium ion battery no matter the lithium ion battery adopts a Jelly-roll structure or a laminated structure. In other words, the area where the lead is soldered to the current collector has a largest thickness in the lithium ion battery. The increased thickness due to the lead is about 1˜5% of the thickness of an assembled lithium ion battery. Therefore, increase of thickness of a lithium ion battery due to the lead has become one of the key actors which limit the energy density of the lithium ion battery.
Chinese patent publication numbers CN 202495523U and CN 201087907Y each discloses a lithium ion battery which defines a recess on a positive electrode and/or the negative electrode to receive a lead therein. The arrangement of the recess on the positive electrode and/or the negative electrode can reduce the thickness of the lithium ion battery. However, when the recess is defined at one end of the positive electrode or the negative electrode along a length direction thereof, thickness variation around the recess is much larger than the thickness variation of the film afar from the recess. Particularly, the arrangement of the recess may generate a number of corners. The film around the corners is readily peeled off, especially when the negative active material adopts an expansive substance, such as silicon. The structure as previously described may lead to a high internal resistance of the lithium ion battery and affect the capacity of the lithium ion battery. In addition, there is no insulating layer provided on the positive area corresponding to the positive recess or the negative recess, internal short circuit and lithium precipitation may potentially occur to the lithium ion battery, which will inevitably affect the safety performance of the lithium ion battery.
In view of the foregoing, what is needed, therefore, is to provide a lithium ion battery having desirable safety performance.